DIYbanter - View Single Post - Furnace Problems - Blowing cold air

Ken[_6_]

wrote:
Thanks Edwin,

If I understand this right, the thermocouple is a sensor which senses
if the pilot flame is hot enough to sustain burning the gasfuel from
the burner, right?

On the ones I have seen, the thermocouple is used to control the pilot
light. In other words, the pilot light will go out if the thermocouple
does not sense the pilot light being on. Therefore it will NOT release
gas to burn, OR to keep the pilot light lit. Yours may be different,
but that is how the ones I have seen work.

That would lead me to believe that the thermocouple is PROBABLY good
since your pilot light stays lit. Check for 24V A/C across the coil of
the gas valve when heat is being called for. No 24V, a problem with the
wiring to, or the thermostat. If you have 24V, remove one lead and
check for an open coil on the gas valve. It happens quite often.

It goes without saying that your gas valve is set to the "ON" position
and not on the "Pilot" position. Being in the pilot position would give
you the symptoms you described. If you do not feel capable of making
these checks, call a serviceman for the furnace. Electricity and gas
are two things you should not mess with unless you are sure of what you
are doing.

So if it's broken, the thermocouple keeps the main gas valve located
in the pilot assembly closed and it shuts off the gas valve to the
burners?

Hm, that makes sense and that is possibly a reason why my pilot is on,
but burner is not.

Is it hard to replace? Where would it be located on this 20 year or
gas furnace, brand: CLARE?
Any idea? Should I do it myself or is there a way to just clean the
thermocouple from dust or something like that to make it work?